As to a conventional air conditioning method in a plant factory, there is an air conditioning method of, for example, Japanese Unexamined Patent Publication No. 2003-52253 as a method of performing air conditioning control over a whole cultivation room by an air conditioner provided on a wall surface, or a method of installing circulation fans in a multistage cultivation shelf to perform air conditioning control over the respective stages in constant flows.
FIG. 6 is a view showing an air conditioning method of Japanese Unexamined Patent Publication No. 2003-52253. An arrow shows a direction of air-flows. Plants are planted and cultivated in cell trays 27 installed in box-shaped raising seedling apparatuses 22. In this air conditioning method, air subjected to cooling and humidity conditioning by an indoor unit 21 of an air conditioning apparatus provided on a wall surface of an enclosed structure 20 is sucked from a front surface side of the box-shaped raising seedling apparatuses 22 by activation of air fans 25 installed in a back surface of a raising seedling shelf 26 to be exhausted to a space between the wall surface of the enclosed structure 20 and the back surfaces of the box-shaped raising seedling apparatuses 22 via air rooms 24. The air exhausted to this space has been heated by heat generated by artificial lighting apparatuses 28, temperature and humidity thereof are readjusted by the indoor unit 21 of the air conditioning apparatus, and the air is repeatedly resupplied to an open front surface side of raising seedling spaces 23 of the box-shaped raising seedling apparatuses 22.
Moreover, generally, the air whose temperature, humidity, and carbon dioxide concentration have been adjusted are supplied to leaves and stems at a proper wind velocity during plant raising, by which transpiration of the leaves in the plants is promoted, and photosynthesis is also promoted.
FIG. 7 is a view showing a correlation between a wind velocity and a transpiration rate described in Studies on the Effect of Wind Speed upon the Photosynthesis (2), The Relation between Wind Speed and Photosynthesis by Kazutoshi YABUKI and Hideo MIYAGAWA, Agricultural Meteorology Vol. 26, No. 3, p. 139, December 1970 thereinafter referred to as “YABUKI et al.”). In an environment of an ambient temperature of 25 degrees, the transpiration rate one hour later in an area 10 cm×10 cm of a central portion of a leaf of a plant is shown, when the wind velocity is changed in the vicinity of the leaf of the plant under three conditions of relative humidities of 50%, 65% and 80%.
Referring to FIG. 7, a minimum wind velocity effective to the transpiration of the leaf of the plant is 0.05 m/sec. Moreover, while an optimum wind velocity differs depending on the humidity condition, the transpiration rate is increased by raising the wind velocity in the vicinity of the plant.